The invention relates to a prosthetic heart valve comprised of a support with a base ring that carries two posts extending axially of the ring, connected by arcuate walls serving for the mounting of two flexible cusps, and having outer edges forming an inside support for the respective cusps, the base ring seen from above having a closed noncircular shape with a major longitudinal axis and two unequal transverse minor subaxes, the posts extending from the major axis and forming transitions from the one to the other half.
Such a mitral heart valve is known from WO 97/49355. In order to avoid a potentially deleterious interference between the functions of the heart and of the valve, it is proposed in this publication that the wall with the smaller arc carry a cusp of smaller surface (mural) area than the wall with the larger arc. The two halves of the base ring thus form a stent body of kidney- or D-shape that is shaped like the natural mitral flap of the heart. In order to reduce the risk of interference and irritation of the heart lining by the support, it has further been suggested to incline the principal flow direction by 10xc2x0 to 25xc2x0, preferably about 15xc2x0, from a perpendicular drawn from the mural cusps. The cusps should form a distinctly funnel-shaped passage with a smaller flow cross section than an aortic valve. Although this system and construction of the mitral heart valve is effective because of its physiologic flow from the auricle into the ventricles and its shortness compared to the hitherto known state-of-the-art systems with a circular or symmetrically elliptical support, turbulence is still present at the valve and occurs in locations in which the inner edge of the stent is undercut by the flow, that is in regions that have set-back edges and which form pockets trapping flow and that create undesired turbulence in the flow.
It is an object of the present invention to improve the described mitral heart valve by altering its shape such that such turbulence-creating undercuts are avoided.
This object is achieved by the prosthetic mitral valve according to claim 1 that is characterized in that a plane including a connecting line joining post tips and the major axis of the annulus of the post base ring is inclined vertically to the plane of the basis ring at an angle of 10xc2x0 to 20xc2x0, preferably 15xc2x0, and the wall with the greater arc carries a cusp having a smaller surface (mural) area and inclined at a stronger angle to the base-ring plane than the wall with the larger arc. In this manner a support is produced whose flow direction defined by the angled walls is inclined at 10xc2x0 to 20xc2x0, preferably 15xc2x0, to a perpendicular from the base-ring plane. In contrast to the D- or kidney-shape of WO 97,49355 the present invention has a 180xc2x0 rotated D- or kidney-shape which produces a physiological flow from the auricle through the valve to the ventricle.
Further embodiments of the invention are describes in the dependent claims.
Thus preferably the flow direction defined by inner surfaces of the support is inclined at an angle from 70xc2x0 to 80xc2x0, preferably 75xc2x0, to a base-ring plane. This means that the support inner surfaces which approach each other in the flow direction are inclined at 15xc2x0 to a plane perpendicular from the base-ring plane and including the post-tip connecting line and planes parallel thereto.
According to a further embodiment of the invention the lengths of the minor subaxes form a ratio of from 1.5:1 to 2.5:1. In particular with a subaxis ratio of about 2:1 the shape is nearly that of a natural mitral valve. The major axis of the two different half ellipses of the support has a length between 10 mm and 45 mm. Preferably the posts are of the same thickness as the walls and are imbedded therein, that is the walls extend up and form posts at the ends of the posts which themselves are preferably rounded. In order not to stress the cusps too much in the attachment zone, according to a further feature of the invention the connecting lines of the cusps with the upper inner edges of the respective walls each lie in a plane.
The particular advantage of the mitral heart valve, in particular over such bioprostheses used to replace mitral heart valves where in practice 50% of the cases require blood thinners for the patient, is that the patient equipped with the mitral heart valve according to the invention can be spared these medications, since the new structure largely eliminates mechanical trauma to the blood.